Enzymes produced by gut bacteria in Zophobas morio larvae may breakdown polystyrene used in packaging and may aid in the recycling of plastics.

Polystyrene may be digested by enzymes generated by gut bacteria in the larvae of the beetle Zophobas morio. The enzymes might be modified to break down plastic in recycling operations.

A recent research discovered that Serratia fonticola bacteria in the stomachs of another species of beetle larvae can devour and digest expanded polystyrene used in packaging.

Researchers have discovered polystyrene-degrading bacterial species in the stomachs of Z. morio larvae, sometimes known as “superworms” due to their large size.

“We are the first ones to use a high-resolution method [to identify] potential polystyrene-degrading enzymes in the microbes of the superworm guts. We could also identify the bacterial lineages that possess these polystyrene-degrading capabilities,” says Christian Rinke at the University of Queensland, Australia.

Pseudomonas aeruginosa and species from the Rhodococcus, Corynebacterium, and Sphingobacterium families were identified as the primary polystyrene-digesting bacterial species by Rinke and colleagues.

They discovered that these microorganisms create hydrolases, which utilize water to dissolve the plastic polymer into styrene monomers, which are subsequently broken down within bacterial cells.

For three weeks, the researchers separated 171 superworms into three groups and fed them either wheat bran, polystyrene, or no food at all. Within a day, the worms started to gnaw their way through polystyrene blocks, according to the researchers.

“We confirmed that superworms can survive on a solely polystyrene diet and even gain a small amount of weight compared to a starvation control group, which suggests that the worms can gain energy from eating polystyrene,” says Rinke. “The polystyrene-reared superworms even completed the entire life cycle, formed pupae and emerged as adult beetles.”

However, the polystyrene-eating superworms grew less than a fourth of the weight obtained by bran-eating larvae, suggesting that ingesting plastic is harmful to their health.

“A possible way to work with the superworms is to provide food waste or agricultural bioproducts with the polystyrene. This could be a way to improve the health of the worms and to deal with the large amount of food waste in Western countries,” says Rinke.

However, the researchers are more interested in developing a superworm-free system that is inspired by insects.

“We will focus on creating a system that mimics the mechanical degradation of plastic by the superworm, followed by further degradation by bacterial enzymes… into metabolites that can then be used by other microbes to produce chemical compounds of higher value, such as the bioplastic polyhydroxyalkanoate,” says Rinke.

“This work is a useful supplement to the research on the degradation of plastics by insect gut microbes and enzymes,” says Jun Yang at Beihang University in China. Nevertheless, further work to tweak the enzymes and optimise the composition of microbial communities for efficient plastic degradation will be needed before application, adds Yang.

“It is still too early to make any predictions about when a bioprocess for polystyrene recycling will be available. It will take time to isolate and characterise these enzymes… and then engineer them to meet the stringent requirements for developing a bio-based recycling process,” says Ren Wei at the University of Greifswald, Germany.

Source: New Scientist

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